Consider valadoc a part of vala's toolchain and therefore let it live in
the main repository.
With this merge there is no need to maintain multiple driver sources since
only one is required from now on.
There is no dependency on gee-0.8 and vala's internal gee copy has made to
be sufficient.
The libvaladoc library will be suffixed with vala's version suffix too.
Besides this renaming the rest of the valadoc file layout is kept the same.
https://bugzilla.gnome.org/show_bug.cgi?id=782782